Successful digital communications often requires an accurate determination of the bit rate of a digital data stream. An accurate bit rate determination would be particularly useful in long haul digital communication systems that use the adaptive, flexible “3R” method of regenerating the amplitude of the digital data stream, reshaping the pulses to remove distortion, and retiming the edges of the pulses for sharper transitions.
In addition, an accurate determination of the bit rate would also be quite useful in a billing system wherein customers are charged for the speed of their digital communications.
To obtain the bit rate, one method is to measure the pulse widths directly. However, at high transmission speeds, such as those prevalent in optical communications, this direct measurement can be difficult to do using digital circuits. Typically, the measurement would be done with a timer that counts clock ticks during the pulse. Several pulse widths would be measured. Different samples would then be compared over time to get the minimum pulse width used by the signal. This comparison would typically be done under microprocessor or digital logic control. For high speed signals, such as optical signals, which are roughly at the limit of counter speeds, it is difficult to count clock ticks and then to compare the times before the next pulse width sample arrives. Therefore, as transmission speeds increase, obtaining an accurate direct measurement of the minimum pulse width is increasingly more difficult.